The present invention relates to improvements in retractile tunnel-shaped or tunnel-type framing or forms for poured concrete having two parallel vertical sides which cooperate with two other corresponding sides. The tops of the parallel sides are connected by a horizontal panel stiffened by omega-shaped sections which are parallel to the planes of the sides, but flexible only in the transverse direction, that is to say being deformable solely around axes which are parallel to the corners or edges of the dihedrons formed by the vertical sides and the horizontal panel. The sides rest on the ground by means of jacks, which ensure downward retractability, and wheels which support the form after it is lowered. The lower portions of the sides are connected by horizontal tie beams, with fine screw-type adjusting, which ensure the horizontal retractability of the bottom of the form. The horizontal panel is supported by articulated beams operable to deform said panel, curving it downward and moving inward the corners of the dihedrons to ensure horizontal retractability of the top of the coffering.
The main problem which the present invention undertakes to solve is to decrease the recurring cost of setting up tunnel-type cofferings or forms for concrete used in industrial construction. Frequent attempts have been made not only to lower the cost, but also to shorten the times of assembly, disassembly and handling. It is important, also, to lower the cost of maintenance by means of a suitable simplification.
Existing U-shaped tunnel-type cofferings, that is to say framing or cofferings which are used to form concrete into two lateral walls and a ceiling, may be divided into two large groups. The first group, which has been used for many years, is the two half-shell type coffering. These cofferings are described in French Pat. No. 1,180,699 dated June 17, 1957, and in its addition No. 73,650 dated May 29, 1958. Improvements are described in French Pat. No. 2,136,400 dated Apr. 11, 1972, and especially in French Pat. No. 2,256,671 dated July 15, 1975, and in its first addition No. 74.39448 dated Dec. 3, 1974. Those latter two patents disclose improvements which made it possible to accelerate the handling and use of cofferings of the two half-shell type. The present invention provides for devices which make possible a similar acceleration in the second group of cofferings which now is going to be discussed.
The second group of tunnel-type cofferings is the one called "retractile cofferings", that is to say forms or framing in which the horizontal panel is made of a single part and can be deformed by curving downward, to bring the two corners of the dihedrons formed by the horizontal panel and the vertical sides closer together. Those cofferings are described in French Pat. No. 1,512,440 dated Dec. 23, 1966, and in its addition No. 95,181 dated June 17, 1968, as well as in French Pat. No. 1,600,108 dated Dec. 30, 1968 and its addition No. 2,079,546 dated Feb. 4, 1970. That type of coffering makes it possible, in addition to permitting the concrete to set rapidly, to quickly decoffer or disassemble the pouring construction, and to move the coffering en masse while maintaining the horizontal panel in a single piece, that is to say eliminating the risk of uneven molding in the center of the poured concrete. The mechanics of maneuvering those cofferings, however, is rather complicated, and another purpose of the present invention is to simplify it. Further, the time for handling those cofferings was long, and a third purpose of the present invention is to accelerate such handling and make it more dependable and more rational.
Another drawback of existing retractile cofferings is in not being able to provide an upwardly concave bend in the ceiling which is being formed by pouring concrete. That is a drawback which the present invention eliminates.